Buckling Resistance of Steel Circular Tubes Strengthened by Welding Cover Plates

Welding under service load generates welding-induced residual stresses and deflection, affecting the stability of compression members strengthened by welding cover plates notably. Hence, the associated stability check is more complicated than that of their unstrengthened counterparts. This paper is aimed to propose a stability design method for such strengthened circular tubular members. A model for the welding-induced residual stress is proposed, and its influence on member stability is evaluated through parametric FE analysis. Results show that, for hot-rolled circular tubes, the column curve used for buckling resistance calculation is reduced from column curve “a” prior to strengthening to column curves “b” and “c” after strengthening, depending on the thickness of strengthening plates. Formulas to predict the welding-induced deflection and equivalent residual imperfection are proposed and validated, and the influence of the equivalent residual imperfection on member stability is evaluated through parametric FE analysis to derive the resistance reduction factor, which is also related to normalised slenderness ratio. Having determined the column curve and resistance reduction factor, a stability design method for strengthened circular tubular members is proposed, which is demonstrated to be more accurate than that codified in Chinese code GB 51367. In addition, the service load-generated stress limit for safe and effective strengthening is put forward.